Cannot attach PDF via web but email attach works fine

V3.6.1 - PostgreSQL

I could have sworn this worked before!

If I send an email to an RT ticket with an attached PDF it becomes a linked attachment in the ticket as expected.

If I try to attach a PDF using the ‘file attach’ in a ticket window it ignores the attachment and I end up with an added comment or reply but no attached file. We’re talking about a 60kB PDF - no monster sized file at all.

I can attach a .gif file of a similar size using the ‘file attach’ in the ticket window and it works just fine.

I turned on debug but see nothing suspicious or helpful in the /opt/rt3/var/log/rt.log file.

Any ideas?